Polymer formation processes generally include a washing/purification step during which the product polymer is separated from solvents, byproducts, processing aids, etc. that are utilized or formed during the polymerization reaction. This separation process can be particularly difficult when considering high-performance polymers that are formed in high boiling temperature solvents, as the product polymer should be separated virtually completely (e.g. greater than 99% purification) from compounds that can include salts, acids, bases, etc. Separation of the product polymer from such compounds can pose waste treatment problems, particularly when the separation process includes formation of large quantities of dilute washing liquor.
High performance polymers that can present such waste treatment problems in purification of the product polymer can include, without limitation, polyaramides polymerized from diamines and diacid chlorides; polycarbonates polymerized from diphenols or diphenozides and phosgene; polysulfones, polyether sulfones, and polyether ketones polymerized from diphenoxides and dihalogenated aromatic hydrocarbons; and polyaryienesiloxanes polymerized from diaryldichiorosilanes and diphenoxides.
Polyarylene sulfides are high-performance polymers that present such purification problems. Polyarylene sulfides are generally formed via polymerization of a dihaloaromatic compound with an alkali metal sulfide or an alkali metal hydrosulfide in a high boiling point organic amide solvent. Following formation, the polyarylene sulfide must be separated from the solvent as well as from byproducts of the formation process and from processing aids, which may include both dissolved and undissolved compounds. For instance, the proportion of residual solvent in the formed polymer should be less than 100 parts per million (ppm). Unfortunately, traditional separation processes that adequately remove the extraneous compounds can generate large volumes of dilute washing liquid, which in turn requires treatment for materials recovery thus increasing both economic and environmental costs of the production process.
Standard methods for separation of a polymer from other compounds have included utilizing heat and reduced pressure to vaporize volatile compounds. Unfortunately, this process is time-consuming as well as costly and nonvolatile compounds may remain with the polymer. Another method that has been utilized is extraction of the polymer slurry with a low boiling point solvent such as acetone. This also introduces added costs as the solvent must be recovered, for instance through an additional distillation process. The more straight forward and simple methods such as repeated washings with solvents are also problematic as they generate a great deal of waste that must in turn be treated.
What are needed in the art are methods, devices, and systems that can be utilized for separation of a product polymer from compounds of formation of the polymer. Devices, methods, and systems that can keep capital costs low and avoid the formation of additional waste would be of benefit.